Production of alkali cellulose



Patented Nov. 25, 1952 PRODUCTION F ALKALI- CELLULOSE Merlyn Herbert Wilcox, John Downing, and James Gordon Napier Drewitt, Spondon, near Derby, England, assignors to Celanese Como-.- ration of America, a corporation of Delaware No Drawing.

Serial No. 51,656. 17,1947;

1 Claim.

This invention relates to the, production of alkali cellulose and of cellulose derivatives formed therefrom.

The term alkali cellulose isgiven to cellulose which has been treated with and retains a caustic alkali, in commercial practice caustic soda, either in chemical combination or in intimate physical admixture, or more probably in both modes. Alkali cellulose is made in large quantities as an intermediate stage in the conversion of cellulose into cellulose ethers and also into viscose solutions. The present invention provides a method of making an alkali cellulose which is particularly suited for subsequent etherification.

The usual method of making alkali cellulose consists in soaking cellulose in a fairly concentrated solution of a caustic, alkali and then draining or pressing the mass or otherwise removing excess of the solution above the amount it is desired to retain. A common form of cellulose employed for this purpose is purified wood pulp, which may first be thoroughly disintegrated so as to form a light fluffy mass, or may be immersed in the caustic alkali solution without being disintegrated, for example in the form of the sheets in which wood pulp is commonly stored and transported.

According to the present invention alkali cellulose which is specially suited for subsequent etherification is produced by mixing, without grinding, cellulose of packing density above lb./cu. ft. with solid caustic alkali. (The term packing density is employed to indicate the weight per unit volume of a substantial quantity of the cellulose in the state of packing which it takes up under ordinary conditions without being strongly compressed, as opposed to the density of individual particles. For the purpose of the present invention it is measured by filling a 100 cc. measuring cylinder with the cellulose, allow-. ing the cylinder to fall 20 times through 2 inches on to a rubber base, then measuring the volume occupied by the cellulose, and finally weighing the cellulose. The term packing density" is employed in he append l im o efine. h density of a cellulosic material mea ured in this manner.)

Preferably the packing density of the cellulose is between 10 and 35 lb./cu. ft., and especially between and 30 lb./cu. it.

While the mixing is carried out in the substantial absence of water, other than that normally present cellulose which is in equilibrium with the atmosphere, there may if desired be present an organic liquid, preiera y of a nature audi Application September 28, 1948, In Great Britain October 2, in amount such that the greater part or substantially all the caustic alkali is, undissolved thereby.

The packing density above 10 lb./cu. it, and preferably 15-30 lb./cu. ft, which cellulose for use in the process of the invention must possess, is considerably higher than that of cellulose in the fluffy for-m obtained by disintegrating sheets of wood-pulp in the usual way. We have found that cellulose of these relatively high paqking densities when mixed without grinding with dry powdered or flake caustic alkali gives an alkali cellulose of substantially uniform composition and properties such as cannot in practice be obtained by mixing the usual fluffy form of disintegrated cellulose sheeting with caustic alkali under the same conditions. We have also found that alkali cellulose made by the process of the invention can be converted into cellulose ethers of a high degree of etherification and capable of yielding solutions of excellent clarity.

Cellulose of the required packing density can be produced from sheets of purified wood pulp (for example a so-ecalled rayon-pulp) by breaking the sheets down, for example in a Banbury mixer or other similar type of machine or by a machine having a cutting action. The machine should be set so as to give a product. which has at least one dimension less than 0.2" and preferably less than about 0.1", for example between about 0.02" and 0.075.

To form the alkali cellulose. the powder or granular or other form of cellulose of packing density above 10 lb./cu. ft. is mixed intimately with dry flake or powdered caustic alkali, with or without an anhydrous organic liquid. This mixing may be effected in a suitable mixing machine, for example a Werner-Pfleiderer mixer, or in some other vessel in which a subsequent treatment or reaction is to be performed; for example when the alkali cellulose is to be etherifled by a process involving the use of pressure, the cellulose and caustic alkali may be introduced into an autoclave provided with a suitable stirrer by means of which they may be thoroughly mixed together. If a cellulose ether of high viscosity is required it is advisable to replace the air in the mixer or the autoclave by nitrogen or some other inert gas before mixing the cellulose and the caustic alkali, but if on the other hand a low viscosity product is required the mixture of cellulose andcaustic alkali may be allowed to age in the presence of oxygen before being subjected to the action of the etheriiying agent.

It is for many purposes, e. g. when the alkali cellulose is to be converted into ethyl cellulose or another cellulose ether, preferable to mix the cellulose with a very high proportion of the solid caustic alkali, for example between 8 and 35 and especially between 10 and molecular proportions of caustic alkali for each glucose residue in the cellulose. Alkali in excess of that required for the subsequent reaction can generally be recovered by known methods from the products of the reaction. For example, when the cellulose is etherified the excess alkali dissolves in the water set free in the etherification, and the concentrated solution so formed can be separated from the cellulose ether produced, if necessary after adding further water to ensure complete solution of the alkali.

The new process is of particular value in connection with the etherification of cellulose in the presence of ether-alcohols, for example the mono-methyl ether of ethylene glycol (monomethyl glycol) and other partial alkyl ethers of glycols and glycerol, as described in U. S. application S. No. 51,655, filed on even date herewith.

Advantageously the ether-alcohol may be present during the mixing of the cellulose with the alkali, whether this is performed in the etherification vessel or in a separate mixer, for example a Werner-Pfieiderer mixer. However, the presence of such a liquid is by no means essential, and alkali cellulose produced simply by mixing the cellulose with the solid caustic alkali in the absence of any added liquid can be etherified with very good results.

In a modification of the process described above the caustic soda, instead of being used in a solid and substantially dry form, may be in the form of an aqueous solution of concentration at least 70% and preferably above 75%, e. g. 80% or more. Such a solution may be warmed if necessary to dissolve all the caustic soda. Alternatively, a saturated solution containing some undissolved caustic soda may be used. When employing the caustic soda under these conditions also, better results are obtained by using a form of cellulose of high packing density than by using the usual fluify form.

The invention is illustrated by the following examples:

Example 1 A purified wood pulp (rayon pulp) in sheet form was broken up and passed through a Banbury mixer set so as to give a granulated product having a packing density of 26 lb./cu. ft. in which the individual particles were less than about 0.1" across. This granular cellulose was mixed with about 2.5 times its weight of dry powdered or flake caustic soda and 20% (of the weight of the cellulose) of mono-methyl glycol was added. The mixture was then passed through a Werner-Pfleiderer mixer, in which it was converted into a crumb-like composition. This composition was transferred to an autoclave provided with a stirrer and with a heating jacket; the air was evacuated and between 10 and 20 moles of ethyl chloride for each glucose unit of the cellulose was pumped in. The autoclave was then heated to 130 C. for 12 hours, the pressure being about 250 lb./sq. in., and after this time the gases and vapours were blown off. The contents of the autoclave were cooled, and the concentrated alkali solution which had been formed was run off from the ethyl cellulose produced. The latter was then washed with water until free from alkali and salt. It, had an ethoxyl content of about 52% and was soluble in benzene, whereas ethyl cellulose made under the same conditions but starting with alkali cellulose made by impregnating fluffy disintegrated wood pulp with a 50% caustic soda solution had an ethoxyl content of about 44%.

The process described in the above example could be modified by mixing the cellulose and caustic soda in the autoclave itself and/or by omitting the mono-methyl glycol. In the absence of the mono-methyl glycol the ethoxyl content was somewhat lower.

Example 2 A rayon pulp in sheet form was broken up and passed through a Banbury mixer set to give a granulated product of packing density about 26 lb./cu. ft. To 10 parts by weight of this granulated pulp '74 parts of caustic soda was added in the form of an aqueous solution. The mixture was passed through a Werner-Pfleiderer mixer, and was then transferred to an autoclave provided with a stirrer and with a heating jacket; the air was evacuated and 50 parts by weight of ethyl chloride was pumped in. The autoclave was then heated to 130 C. for 12 hours, and after this time the gases and vapors were blown off. The contents of the autoclave were cooled, and the alkali solution run off from the ethyl cellulose produced, which was then washed with water until free from alkali and salt.

The process of this example could be modified by mixing with the cellulose, before its treatment with the alkali solution, 12-30% of its weight of mono-methyl glycol (which gave a product of somewhat higher ethoxyl content), and/or by mixing the cellulose and alkali in the autoclave instead of in the Werner-Pfleiderer.

Example 3 Wood pulp cellulose of packing density 26 b./cu. it. produced as described in Example 1 was mixed with an equal weight of flake caustic soda and 20% (on the weight of the cellulose) of mono-methyl glycol was added. The mixture was passed through a Werner-Pileiderer mixer and thence to an autoclave provided with means for circulating gases therethrough. The contents of the autoclave were heated to 80-90 C., and methyl chloride was circulated through the autoclave under a pressure of '70 lbs/sq. in. for about 4 hours. The autoclave was then cooled and the methyl cellulose formed washed free from alkali and salt with hot water. It had a methoxyl content about 36%, was soluble in cold water, and dissolved to give a smooth solution in 80/20 methylene chloride/methanol.

A methyl hydroxy-ethyl cellulose could be made by passing ethylene oxide through the autoclave before the methyl chloride.

Example 4 parts of wood pulp cellulose of packing density 26 1b./cu. ft. produced as described in Example 1 was mixed with an equal weight of flake caustic soda and with 20 parts of monomethyl glycol, and the mixture passed through a Werner-Pfieiderer mixer. 53 parts of chloracetic acid was then added, and the mixture was kneaded for about 16 hours at a temperature of 45 C. The product was dissolved in the minimum quantity of water, and the carboxy-methyl cellulose formed was precipitated with alcohol.

Alkali cellulose made by the new process is 5 also of value for the production of other cellulose ethers, for example benzyl cellulose, and mixed others such for example as ethyl hydroxyethyl cellulose and methyl ethyl cellulose. It can also be used for the production of other cellulose derivatives, for example viscose solutions.

Having described our invention, what We desire to secure by Letters Patent is:

A process for the manufacture of alkali cellulose, which comprises breaking down a sheet of Wood pulp cellulose into a particulate form in which the particles have at least one dimension less than 0.2" and which has a packing density of 15 to 30 1b./cu. ft., and mixing without grinding 1 molecular proportion of the cellulosic product so obtained reckoned as 1 anhydro-glucose unit with 8 to 35 molecular proportions of solid caustic soda as the only other reacting substance and in a substantially anhydrous environment in the presence of 5% to 30% of a liquid mono- 6 alkyl ether of a glycol calculated on the weight of the cellulose.

MERLYN HERBERT WILCOX. JOHN DOWNING. 5 JAMES GORDON NAPIER DREWITT.

REFERENCES CITED The following references are of record in the file of this patent:

10 UNITED STATES PATENTS Number Name Date 1,469,824 Seel Oct. 9, 1923 1,683,681 Lilienfeld Sept. 11, 1928 15 1,980,988 Ellsworth NOV. 20, 1934 2,067,946 Picton Jan. 19, 1937 2,138,757 Collings et a1 Nov. 29', 1938 2,145,862 Collings et a1 Feb. 7, 1939 2,176,678 Nevroth Oct. 17, 1939 20 2,553,695 Wilcox et al May 22, 1951 

